A read channel integrated circuit (IC) is one of the core electronic components in a modern hard disk drive. For example, in a magnetic recording system, a read channel converts and encodes data to enable the magnetic recording heads to write data to the disk drive and then read back the data accurately. The disks in a drive have many tracks on them and each track consists of mostly user or “read” data sectors as well as “servo” data sectors embedded between the read sectors. The information recorded in the servo sectors helps to position the magnetic recording head on track so that the information stored in the read sectors is retrieved properly.
Repeatable run out (RRO) refers to a phenomenon that occurs due to an imperfect spindle upon which the magnetic disk rotates that causes the magnetic disk to spin improperly at the center. If the disk is not rotating at the center, the magnetic recording head will not see a circular trajectory and hence will not be on-track to read the servo information properly. A similar phenomenon occurs when spindle imperfections were present when the servo information was written to the magnetic disk. Even though the disk may spin properly in a different hard disk while reading the servo information, the read head might not be able to read the servo information accurately since the information was not written properly on a circular track.
The “servo” data embedded between each read sector includes an RRO data field that helps to compensate for the known Error. The RRO data is used to properly guide the head to come on-track and thereby compensate for the spindle imperfections. The RRO data, however, is not recorded with a preamble field. Thus, the proper sampling phase (timing) to read the RRO information is not known. From a signal processing point of view, the problem of reading RRO information can be thought of as an “asynchronous” data detection problem. Also, the RRO address mark detection is more prone to false detections because the RRO detector starts looking for the RRO data without proper sampling phase (no preamble to guide the timing loop) and the RRO address mark only consists of a few bits. Such an adverse operating environment for RRO detection makes it challenging to properly detect the RRO data. The presence of signal asymmetry in the RRO field makes it even more challenging to detect RRO data.
A need therefore exists for a method and apparatus for compensating for signal asymmetry when detecting data.